The present invention relates to a liquid detection device suitable for detecting the liquid (ink) level or the like in a liquid consumption device such as an inkjet recording device, a liquid container including the liquid detection device, a method of producing a liquid detection device, and the like.
As a typical example of a liquid consumption device, an inkjet recording device including an inkjet image recording head is known. Further examples of a liquid jet device include a device including a color material jet head used to produce a color filter for a liquid crystal display or the like, a device including an electrode material (conductive paste) jet head used to form an electrode for an organic EL display, a field emission display (FED), or the like, a device including a bio-organic substance jet head used to produce a bio-chip, a device including a sample jet head as a precision pipette, and the like.
In an inkjet recording device as a typical example of a liquid consumption device, an inkjet recording head which has a pressure generation means that pressurizes a pressure generation chamber and a nozzle opening which discharges a pressurized ink as an ink droplet is secured to a carriage. An ink contained in an ink container is successively supplied to the recording head through a passage so that successive printing can occur. The ink container is formed as a removable cartridge which can be easily exchanged by the user when the ink has been consumed, for example.
As a method of managing ink consumption of the ink cartridge, a method which manages (calculates) ink consumption by integrating the number of ink droplets discharged from the recording head or the amount of ink sucked up by maintenance by means of software, a method which manages the time when a specific amount of ink has been consumed by incorporating a liquid surface detection electrode in the ink cartridge, and the like have been known.
However, the method which manages ink consumption by integrating the number of ink droplets or the amount of ink by means of software has the following problem. Specifically, a head may have a variation in weight of ink droplets discharged. Such a variation in weight of ink droplets does not affect image quality. On the other hand, the ink cartridge is filled with an excess amount of ink taking into account the case where an ink consumption error is accumulated due to a variation. Therefore, the ink remains depending on the product.
According to the method which manages the time when a specific amount of ink has been consumed utilizing an electrode, since the actual amount of ink can be detected, the ink level can be managed with high reliability. However, since the liquid surface of the ink is detected utilizing the conductivity of the ink, the type of ink which can be detected is limited. Moreover, the electrode seal structure becomes complicated. Since a noble metal having high conductivity and corrosion resistance is generally used as the material for the electrode, the production cost of the ink cartridge increases. Furthermore, since it is necessary to provide two electrodes, the number of production steps increases, whereby the production cost increases.
A device developed to solve the above-mentioned problems is disclosed in JP-A-2001-146030 as a piezoelectric device (hereinafter referred to as “sensor unit”). This sensor unit monitors the ink level in an ink cartridge utilizing a phenomenon in which the resonance frequency of a residual vibration signal caused by residual vibrations (free vibrations) of a diaphragm after forced vibrations changes depending on whether or not ink exists in a sensor cavity opposite to the diaphragm on which a piezoelectric element is stacked.
JP-A-2006-281550 discloses technology in which a metal sensor base provided with a sensor chip including a piezoelectric element is disposed in an opening in a unit base and sealed with a film. The sensor base of the unit base is disposed to face an ink supply passage of an ink container. In this case, the unit base is liquid-tightly disposed in the ink container through a sealing rubber. In order to ensure liquid-tight properties using the sealing rubber, a spring which presses the unit base against the ink container side is provided.
FIG. 7 or 12 of JP-A-2006-315302 discloses a structure in which a sensor base is supported at three points (i.e., partition wall and right and left walls of a casing main body). JP-A-2001-328277 discloses technology in which a breakwater wall is provided in a liquid opposite to a sensor so that bubbles enter a sensor cavity to only a small extent even if bubbles occur on the liquid surface in a tank.
The technology disclosed in JP-A-2006-281550 can implement the detection principle disclosed in JP-A-2001-146030. However, it is necessary to provide the unit base separately from the ink container, and the sealing rubber and the spring are indispensable to liquid-tightly secure the unit base in the ink container.
Therefore, the technology disclosed in JP-A-2006-281550 increases the number of parts and complicates assembly for liquid-tightly securing the unit base using the sealing rubber.
Since the unit base is formed by double-molding polypropylene and an elastomer, cost increases.
According to the technology disclosed in JP-A-2006-315302, since vibrations of the piezoelectric element are absorbed by the casing main body that comes into contact with the sensor base at three points, it is difficult to obtain sufficient vibrations which can be detected by the piezoelectric element. Moreover, since the sensor base is positioned utilizing an opening formed in the casing main body, bubbles remain in a minute gap around the sensor base during ink injection, whereby an ink end state may be erroneously detected. This cannot be prevented even when using the breakwater wall disclosed in JP-A-2001-328277. Specifically, the breakwater wall blocks the flow of the ink when initially injecting the ink, whereby bubbles are likely to occur around the sensor base.
Some aspects of the invention may provide a liquid detection device which enables a reduction in the number of parts, a liquid container including the liquid detection device, and a method of producing a liquid detection device.
Other aspects of the invention may provide a liquid detection device which has a structure that can increase an amplitude during liquid detection, a liquid container including the liquid detection device, and a method of producing a liquid detection device.
Further aspects of the invention may provide a liquid detection device in which erroneous detection is suppressed by employing a structure which rarely allows bubbles to remain around a sensor base when introducing a liquid, a liquid container including the liquid detection device, and a method of producing a liquid detection device.